Cellular telephones currently continuously transmit during a telephone call. In a typical scenario, a subscriber unit moves throughout a cell while constantly maintaining communication with a base station located approximately in the center of the cell. As the subscriber unit moves throughout the cell, the received signal strength indication (RSSI) as seen by the base station, varies significantly. This variance has the potential to overload the receiver in the base station when the subscriber unit is very close to the base station.
As personal communication networks (PCN) and code division multiple access (CDMA) type cellular systems evolve, the dynamic range requirements on transmitters becomes more stringent. To avoid overloading of the base station receiver when a subscriber unit is very close to the base station, the subscriber unit must have a typical dynamic range upwards to approximately 80 dB. All current approaches to PA power control, however, are limited to around 40 dB dynamic range because stray RF coupling limits the amount of attenuation that can be achieved to about that level. Stray radiation also becomes a problem when attenuation levels between 40-80 dB are attempted.
Thus, a need exists for power control circuitry which achieves a wide dynamic range while overcoming the problems of stray RF coupling and stray radiation.